About 55.6 million years ago, during the Paleocene-Eocene Thermal Maximum (PETM), global warming sped out of control. As the atmosphere's carbon levels rose, so did sea levels and temperatures, which jumped by 46.4 degrees Fahrenheit. Many species either struck out on massive migrations or went extinct
Though this period is one of the best geologic representations of what climate change is doing to the planet today, researchers still don't know why it happened, reports Sarah Kaplan for The Washington Post. Some argue that the rise in carbon took place over 5,000 to 20,000 years and could have come from volcanic activity. Others believe a change in Earth’s orbit or a change in ocean currents could have triggered the upward march of temperatures.
In 2003 researcher Dennis Kent of Columbia University suggested that a comet impact could have triggered such a rapid warming event. Now, he and his colleagues present potential evidence that a comet did indeed set off the PETM.
In a new paper published in Science, Kent suggests that tiny glass spheres called microtektites found along the coast of New Jersey are signs that a comet hit earth around the time of the Thermal Maximum. Microtektites are thought to form from massive extraterrestrial impacts with Earth, which spray the beads of rapidly cooling molten glass and quartz out from the impact zones.
Morgan Schaller, lead author of the study and researcher at Rensselaer Polytechnic Institute, found the sand-grain sized glass beads in core samples collected in suburban Millville and Wilson Lake, New Jersey, in a stream bed in the town of Medford and in a core taken from the deep sea bed near Bermuda. Each of them contain the dark beads in the layer associated with the start of the PETM.
Schaller wasn’t originally on the hunt for evidence of a comet strike at all, reports Paul Voosen at Science. Instead, he and graduate student Megan Fung were hunting the Jersey shore for fossils of microorganisms called foraminifera, which can be used to date sediments, when they encountered the microtektites.
The team concluded that the spheres came from an extraterrestrial impact, and a layer of charcoal above and below the stratum containing the beads indicates a time of immense wildfires, which would have occurred after a comet hit. Schaller believes the amount of carbon introduced by the comet would have been immense.
“It’s got to be more than coincidental that there's an impact right at the same time [of the PETM],” Schaller says in the press release. “If the impact was related, it suggests the carbon release was fast.”
Not everyone is convinced by the evidence. Ellen Thomas, a geologist at Wesleyan University in Middletown, Connecticut, tells Voosen she has re-examined cores taken at the PETM boundary in New Jersey and globally and has found no spherules. If the researchers are able to definitively date the beads, she says she’ll be convinced. Otherwise she believes the microtektites may come from other layers and possibly contaminated the PETM layers during the drilling process.